1. Field of the Invention
The present invention relates generally to the construction of bullet trapping backstops, and, more particularly, to covering loose-particulate projectile backstops.
2. Background Description
In order to maintain proficiency in the use of firearms, it is common to engage in target practice on a training range. Of great concern on a training range is the prevention of ricochets. To this end, outdoor ranges often use a large dirt berm behind the target to decelerate and trap the bullet. There is also a growing desire to build shooting ranges within enclosed structures. This permits frequent use of the range regardless of weather and without excessive travel time. Obviously, use of a dirt berm behind the target is impractical for indoor ranges.
For both indoor and outdoor use, current trends in bullet containment systems focus on two different types of systems. The first, often called a bullet stop and containment chamber, has a pair of plates that channel bullets toward an opening in a containment chamber. Inside the containment chamber are impact plates that slow the bullet to a stop. Unfortunately, such systems are relatively expensive and difficult to manufacture and maintain.
The second, more common type of containment system is the bullet backstop or bullet trap system. Bullet backstops typically include a back plate made of steel inclined to the line of fire. The upper surface of the back plate is covered with a layer of loose particulate material as a medium for decelerating and trapping incoming bullets. This layer is several feet thick in the direction the bullet travels. The impact material is typically a resilient granular material. As bullets impact the material, they will decelerate sufficiently such that, if they do impact the back plate, any ricochet will be minimal. A number of bullet traps utilize rubber chunks or chips as the impact material. For example, U.S. Pat. No. 6,378,870 to Sovine (“the '870 Patent”) teaches the use of relatively large rubber nuggets disposed along a plane inclined to the line of fire, while U.S. Pat. No. 5,848,794 to Wojcinski et al. (“the '794 Patent”) discloses a similar bullet trap using relatively small rubber granules disposed along an inclined plane.
However, incoming rounds tend to dislodge the loose particulate matter, splashing and scattering it about the trap, and throwing some loose particulate out of the trap altogether. Furthermore, the vibrations induced by incoming rounds will cause the particulate to stuff. The combination of splashing, scattering, and sluffing reduces the thickness of the particulate layer in the direction the bullet travels, particularly in the area directly behind the target. This in turn increases the likelihood of ricochets off the back plate. Higher impact velocities compound these problems.
While traps of reduced slope may diminish sluffing, they do so at the expense of increasing the size of the trap along the line of fire. Furthermore, reduced-slope traps remain susceptible to splash and scatter. Thus, to ensure a safe thickness of particulate, it remains necessary to periodically rake dislodged particulate back into place or otherwise replenish the trap.
To address splashing and scatter of loose particulate, extant systems, such as that disclosed in U.S. Pat. No. 5,901,960 to Nesler et al. (“the '960 Patent”), often utilize a membrane of elastomer, fabric, or netting to cover the particulate. Since the membrane is thin and light, it must somehow be anchored in place, typically by attachment to the back plate or other support structure. While the membrane reduces the occurrence of splash and scatter, the particulate beneath the membrane remains susceptible to sluffing. Since the membrane does not serve to decelerate incoming rounds, rounds may impact the back plate with sufficient velocity to ricochet if the particulate beneath the membrane is not carefully monitored to ensure it remains at a thickness sufficient to completely decelerate and trap incoming rounds.
After a number of firing sessions, the portion of the membrane in the target zone will be destroyed and no longer capable of restraining the loose particulate. Though the remainder of the membrane may still be viable, it is necessary to replace the entire membrane. Alternatively, the destroyed portion could be repaired with a patch. If patching is preferred, the trap must be taken out of service until the patch cures, and some solvents used in patching have been known to cause fires.